Traditionally, nickel and copper ore concentrates are processed in separate smelting processes. Nickel and copper mattes are produced from these concentrates by means of, for instance, a flash smelting process. After smelting, the recovery of each metal from the matte produced is carried out by hydrometallurgical processes based on the prerequisites of the metal in question.
A matte resulting from a pyrometallurgical process needs to be disintegrated in one way or another before it is subjected to hydrometallurgical processing. It is a common practice to granulate molten matte by jetting pressurized medium, which may be, for instance, air or water, against a stream of molten matte falling from a launder. U.S. Pat. No. 4,671,752 A discloses an apparatus for air-pulverizing high-temperature molten slag. U.S. Pat. No. 6,000,242 A discloses an apparatus and a method for granulating molten material by means of water, which is pH controlled to neutral or slightly basic. U.S. Pat. No. 7,857,887 B2 discloses a matte granulation method in which gas is sprayed on a molten matte flowing out from a chute so that the gas jet disperses the molten matte into tiny liquid drops. The gas also cools the liquid drops to semi-molten or solid matte grains. The matte grains are quenched by pressurized cold water. The gas is pressurized and inert with the molten matte. The gas can be saturated steam or compressed air with a gas pressure of 0.2-3.0 MPa.
U.S. Pat. No. 3,880,653 A and U.S. Pat. No. 6,569,224 B2 teach subjecting nickel and copper containing matte or concentrate to chlorine leach. It is also known from the prior art to use pressure leach in a sulfate environment. Nickel is reduced to metal by nickel electrolysis on nickel cathodes. Electrolytic deposition of nickel from a purified solution can be carried out by chloride electrolysis, as taught in U.S. Pat. No. 3,085,054 A, U.S. Pat. No. 3,880,653 A and U.S. Pat. No. 3,975,189 A, or by sulfate electrolysis. Metallic nickel can also be produced by hydrogen reduction in autoclaves. Copper is extracted and electrowon on copper cathodes.
The above mentioned patents aim at leaching of copper-nickel matte in a chloride environment, purification of the solution by precipitation/extraction and, finally, electrolytic deposition of nickel on cathode. The methods of the prior art also produce ferrous leach residue, which is removed from the process by dumping. The process of U.S. Pat. No. 6,569,224 B2 is directed to treatment of concentrate. In that case, precious metals are bound to sulfur and its compounds, which leads to losses of precious metals.
Today, granulation of matte and leaching of metals from matte are carried out in separate process steps. Granulation is usually carried out with a slightly alkaline liquid and leaching is carried out as a combined atmospheric and pressure leaching. The inventors have realized that there is a need for a new process that combines these two process steps.